This invention relates to the manufacture of ceramic articles and more particularly to the manufacture of bilayered green ceramic tapes having a corrugated first layer and a substantially flat second layer bonded thereto. As is well known in the art, ceramics are considered premium materials of construction for several uses in that they are highly resistant to heat and most forms of erosion and corrosion. Several examples of uses of ceramics include heat exchanges for waste heat removed from exhaust gases, supports for catalysts for the automotive catalytic muffler, and similar uses where the atmosphere is both hot and corrosive. Many of the above ceramics are produced utilizing a multi-step process during which the basic ceramic compositions are prepared in a slurry state, the slurry ingredients are treated, i.e. ball milled, after which the slurry is cast into a tape using what is known in the art as a doctor blade. The blade is adjusted to give a desired thickness of tape. For many uses, the resulting thickness of this final ceramic green tape is approximately 5 to 7 mils.
After casting the tape, the solvent which comprised one of the components of the slurry is then evaporated resulting in a now workable green product.
A previous problem inherent in many of the green ceramic tapes of the prior art has been the inability of the corrugated first layer to maintain its established shape after subsequent bonding to the flat adjoining layer. Usually such deformation occurred when the article was rolled into a cylindrical shape or stacked in established columns.
A well known method for maintaining the corrugated layer in its desired shape has been to utilize a thin sheet of aluminum foil as a support member. This method, however, is limited to those ceramics in which the raw material has a metal foil because the foil is the major contributor to the strength of the green film.
To assist in solving the above-described problem, there are disclosed in U.S. application Ser. No. 313,102 formulations for self supporting ceramic tapes which, when subsequently subjected to a proper forming process, will overcome the above-cited disadvantages of prior art ceramic articles. These formulations consist essentially of sinterable solid particles of ceramic raw materials substantially uniformly distributed throughout a supporting media. The weight of the supporting media to these materials is in the ratio of from about 1:3 to about 1:6. The media consists essentially of a thermoplastic resin, a plasticizer, an organic solvent and a deflocculant, each established within the described media according to specified percentages.
To form these and similar green tape compositions into the configurations desired has thus resulted in the development of a new process.
It is believed therefore that a process which will result in the production of a bilayered green ceramic tape having a corrugated first layer and a substantially flat second layer bonded thereto without the necessity for requiring additional items such as aluminum foil supports while still assuring that the resulting tape will maintain its desired configuration after bonding would be an advancement in the art.